The 2009 Fermi Symposium

Washington, DC, USA
2009 November 2–5

The clumpy wind of Vela X-1

Felix Fürst, Jörn Wilms, Ingo Kreykenbohm, Katja Pottschmidt, Manfred Hanke, Richard E. Rothschild, Peter Kretschmar, Norbert Schulz, David P. Huenemoerder, Dmitry Klochkov, and Rüdiger Staubert

The structure of the accreted mass in the HMXB Vela X-1, consisting of a neutron star and the high mass donor star HD 77581, is investigated by analyzing the flaring behavior in X-rays.
To this end we analyzed all archival INTEGRAL data, calculating the brightness distribution in the 20–60 keV band. We show that the emerging distribution is closely following a log-normal distribution. Orbital resolved analysis shows that the structure in the accretion region is strongly variable, explainable by shocks and an accretion wake. Analysis of RXTE ASM data shows a strong orbital change of NH. Derived accreted clump masses from the INTEGRAL data are of the order of 1020–1021 g. We show that the lightcurve can be described using a model of multiplicative random numbers.
In course of the simulation we calculate the Power Spectral Density of the system in the 20–100 keV energy band and show that it follows a red-noise power law.
We conclude that a mixtures of a clumpy wind and shocks and turbulences can explain the measured distribution.